The processing of the surfaces of organic materials represented by polymer materials, for example, using an excimer laser that oscillates high-intensity pulsed light in the ultraviolet region, is under active study as precision surface processing and precision surface machining of organic materials, from both basic and application points of view.
On the other hand, to improve the biocompatibility of the surfaces of polymer articles used for artificial internal organs, sensors, etc., in the medical field is an important subject for improvement of the lifetime and reliability of implant-type artificial internal organs and implant-type sensors. Various investigations have been made so far, but under present conditions, practically endurable effective processing techniques have not yet been found. This is because various properties needed for artificial internal organs and sensors, such as mechanical strength (toughness) and durability, tend to be incompatible with biocompatibility. That is, polymer materials excellent in biocompatibility (e.g. biopolymers) are often low in mechanical toughness and cannot be used as articles. On the other hand, polymer materials excellent as articles are inferior in biocompatibility and therefore cannot be implanted as medical materials in the body for a long period of time.
Accordingly, under present conditions, materials having both properties to a certain extent are currently used, tentatively. Under these conditions, a conceivable method for improving biocompatibility of the surfaces of polymer articles is to chemically coat the surfaces of an article excellent in mechanical toughness with a substance excellent in biocompatibility. Since biocompatibility depends on surface properties, by coating the surface thinly with a substance excellent in biocompatibility through chemical bonds between the surface and the substance, the biocompatibility of an article can be improved without detriment to the other properties of the article.
Kaetsu reported a method for immobilizing polysaccharides on the surfaces of a polymer article by irradiating the polymer article with light from an ultraviolet lamp in an aqueous solution of a mixture of polysaccharides and a photopolymerization initiator, to initiate a crosslinking reaction by the initiator (Nucl. Instr. and Meth. in Phys. Res., Vol. B105, p 294 (1995)). This method is successful in immobilizing polysaccharides that are one type of biopolymers excellent in biocompatibility on the surfaces of an article, to improve the biocompatibility of the surfaces of the article. However, since, in this method, the crosslinking reaction by the photopolymerization initiator takes place randomly in solution, the thickness of the film of the polysaccharides immobilized on the article surfaces becomes increased, leading to the disadvantages that the mechanical properties of the article are lowered, and that the photopolymerization initiator inevitably remains in the modification layer as impurities.
The present inventors proposed methods for effectively modifying the surfaces of a polymer article by ultraviolet laser processing (JP-A-4-183873 ("JP-A" means unexamined published Japanese patent application), JP-B-7-5775 ("JP-B" means examined Japanese patent publication), and JP-B-7-5777). With these methods, it is found out that, for instance, since active species are produced on the surfaces of an article by irradiation with a laser, an organic compound having a functional group, such as an azide group, a vinyl group, and an acetylene group, can be introduced on the surfaces of the article, to react with the active species on the surface, so that the organic compound can be immobilized through chemical bonds on the article surfaces irradiated with the laser beam. According to these methods, an organic compound, different from those constituting the article can be immobilized onto the surface of the article, without using photopolymerization initiators that will become an impurity.